In a telecommunication network described by a 3rd Generation Partnership Project (3GPP), a charging system is one of the important functional components of the telecommunication network and is an important guarantee for an operator to implement revenue. FIG. 1 is a connection diagram of charging functional entities in a 3GPP network, and the function of each charging functional entity as shown in FIG. 1 is described as follows.
A Charging Trigger Function (CTF) is embedded in each network element (including an access layer network element, a control layer network element and a service layer network element) of a 3GPP IMS to implement the following major functions: acquisition of charging information according to monitored use conditions of network resources and transmission of an Accounting Request (ACR) message to a Charging Data Function (CDF) through a Rf interface (Offline Charging Reference Point).
The major functions of the CDF are to receive the ACR message from the CTF, to construct the ACR message into a Charging Data Request (CDR), and to send the CDR to a Charging Gateway Function (CGF) through a Ga interface.
The major functions of the CGF are to store and manage the CDR received from the CDF and send a CDR file to a Billing Domain (BD) through a Bi interface.
FIG. 2 is a network architecture diagram of an IMS system (the figure only shows an example of an IMS network because the architecture of the IMS network is not limited to such architecture due to the diversity of actual User Equipments (UEs) and access equipments). As shown in FIG. 2, in a session of a user, signaling passes through network elements including a Proxy Call Session Control Function (PCSCF), a Serving Call Session Control Function (SCSCF), an Interrogating Call Session Control Function (ICSCF) and an AS. The CTF of each network element sends ACR[Start] when a session is started, sends ACR[Stop] when the session is ended, and triggers ACR[Interim] according to a Session Initiation Protocol (SIP) event during the session. The CDF opens a Charging Data Record (CDR) when having received the ACR[Start], updates the CDR when having received the ACR[Interim], and closes the CDR when having received the ACR[Stop].
In the CDR of each network element, a CDR of a PCSCF is from the PCSCF where a place visited by a user locates, and is generally applied to roaming settlement; a CDR of an A is from the AS subscribed by a user with rich charging information including specific service information, and is generally applied for user charging; and a CDR of an SCSCF is from the core control network element SCSCF of the IMS, and is generally applied to charging association or account checking etc.
In practical IMS network deployment, the aforementioned network elements are indispensable. A session of a user is generally performed through the aforementioned network elements. If there is an abnormality in a certain AS or there is an abnormality in a network connection between an SCSCF and a certain AS, the SCSCF will determine, according to configuration, to continue or end the session. If the session is continued, i.e., an abnormal AS is bypassed by the SCSCF, subsequent processing is continued to be performed. If the session is terminated, i.e., the SCSCF terminates a call request, session establishment fails.
FIG. 3 shows the condition that an SCSCF bypasses an AS. It is assumed that a UE (A) calls a UE (B), after there is an abnormality in an AS (A), an SCSCF (A) determines that there is a failure in the AS (A), and does not trigger an AS (A) service subscribed by a calling party. If there are other subscribed AS services, other AS services are triggered continuously, and then a calling request is sent to a called side network. After there is an abnormality in an AS (B), an SCSCF (B) determines that there is a failure in the AS (B), and does not trigger an AS (B) service subscribed by a called party. If there are other subscribed AS services, other AS services are triggered continuously, and then a calling request is sent to the SCSCF (B). Subsequent processing is performed in a similar manner.
It may be learned from the above analysis that, if a session is connected continuously in the case of an abnormality occurring to the AS, the possibility of an amount of service interruptions can be reduced greatly, thereby guaranteeing the call rights of a user to the highest degree and further improving the degree of satisfaction of the user. This is a solution which most operators are pleased to adopt. However, based on the prior art, since an abnormal AS fails to generate a corresponding CDR for a session in which a bypass is performed by an SCSCF in the case of the abnormality occurring to the AS, the session will not be charged if user charging is performed according to the CDR of the AS, thus resulting in inaccurate charging. In addition, the accuracy of subsequent processing including operation and maintenance analysis may be also reduced if the abnormality condition of the AS is not learned.